Video signal magnetic recording and/or reproducing apparatus with automatic mode discrimination

ABSTRACT

The invention relates to a mode discrimination circuit for use in a magnetic recording and/or reproducing apparatus. A reproduced luminance signal FM wave is applied to a bandpass filter which passes the frequencies which are in the vicinity of a tip of a synchronizing signal of the standard mode. The output of the bandpass filter is applied to an envelope wave detection circuit which provides a detected output. The detected output is applied to a hold circuit which holds the detected output for a predetermined period of time to thereby output a signal indicative of a standard or high band recording mode of the reproduced luminance signal FM wave.

FIELD OF TECHNOLOGY

The present invention relates to the discrimination of an FM carrierfrequency in a video signal magnetic recording and/or reproducingapparatus (hereinafter referred to as VCR).

BACKGROUND ART

FIG. 3 illustrates a frequency allocation for the standard modedescribed in a handling manual of, for example, the VCR of Sony make,HF-900 (hereinafter referred to as the conventional apparatus), wherein1 represents a luminance signal FM wave, 2 represents a low frequencyrange conversion chroma signal, 3 represents an FM carrier frequency(3.6 MHz) of a sync signal tip, and 4 represents an FM carrier wave (4.8MHz) of a white peak. FIG. 4 illustrates a frequency allocation of ahigh band mode, wherein 1a represents a luminance signal FM wave of thehigh band mode, 3a represents an FM carrier frequency (4.4 MHz) of async signal tip, and 4a represents an FM carrier frequency (5.6 MHz) ofa white peak.

In the above described conventional apparatus, according to the standardmode, at the luminance signal FM wave 1, the FM carrier frequency 3 ofthe sync signal tip is 3.6 MHz, and the FM carrier frequency 4 of thewhite peak is 4.8 MHz. On the other hand, according to the high bandmode, the FM carrier frequency 3a of the sync signal tip is 4.4 MHz andthe FM carrier frequency 4a of the white peak is 5.6 MHz.

Although in the VCR the frequency characteristics of the FM wave must bemodified where the carrier frequency of the luminance signal FM wave isto be changed, the conventional apparatus is so designed that thefrequency characteristics of the reproduced FM wave are modified byverifying a reproduced image on a monitor TV with sight and then bymanually operating a change-over switch. Accordingly, it may happen thatat the high band mode the change-over switch may be connected to thestandard mode position, and in that case, there has been a problem inthat the reproduced image tends to be disturbed.

SUMMARY OF THE INVENTION

The present invention has been developed with a view to eliminating theabove discussed problem and has for its object to provide a video signalmagnetic recording and/or reproducing apparatus which is able toautomatically discriminate the high band mode and to then automaticallyswitch the mode over during reproduction.

The VCR to which the present invention pertains is one which is providedwith a bandpass filter capable of allowing to pass therethrough only afrequency in the vicinity of a tip of a synchronizing signal of theluminance signal FM wave modulated by a carrier of predeterminedfrequency, a wave detecting circuit for carrying out an envelope wavedetection of an output from the filter, and a discriminating circuit fordiscriminating the high band mode in reference to an output from thewave detecting circuit.

In the present invention, the discrimination is carried out by thebandpass filter through which only the frequencies in the neighborhoodof the sync signal tip portion of the luminance signal FM wave can pass,and the high band mode can be discriminated by the envelope wavedetection of a signal which has passed.

According to the present invention, since the discrimination of the highband mode is carried out by means of the bandpass filter through whichonly the frequencies in the neighborhood of the tip of the synchronizingsignal of the luminance signal FM wave can pass, and then by effectingthe envelope detection of the signal which has passed therethrough,there are such effects that a highly precise mode discrimination can beaccomplished with the simple and inexpensive apparatus and by theutilization of the result of such mode discrimination the modechange-over can be carried out automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are notlimitative of the present invention, and wherein:

FIG. 1 is a block circuit diagram illustrating a construction of themode discrimination of the VCR according to one embodiment of thepresent invention;

FIG. 2 is a diagram illustrating waveforms of signals of the embodimentof the present invention;

FIG. 3 is a diagram illustrating the frequency allocation for thestandard mode in the VCR; and

FIG. 4 is a diagram illustrating the frequency allocation for the highband mode.

DETAILED DESCRIPTION

Hereinafter, one embodiment of the present invention will be describedwith reference to the drawings. In FIG. 1, reference numeral 5represents a reproduced luminance signal FM wave, and reference numeral6 represents a bandpass filter (BPF), the bandpass range of which is soselected as to permit only a frequency in the vicinity of the syncsignal tip portion of the reproduced luminance signal FM wave to passtherethrough. Reference numeral 7 represents a BPF output, referencenumeral 8 represents an envelope wave detecting circuit, referencenumeral 9 represents a wave detected output, reference numeral 10represents a hold circuit, and reference numeral 11 represents a highband discriminating signal. FIG. 2 illustrates respective waveforms ofvarious signals of the above mentioned circuit and, in this drawing, 12represents a reproduced luminance signal.

The BPF output 7 of the sync signal tip portion of the reproducedluminance signal FM wave 5 can be obtained during the standard modethrough the use of BPF 6, through which only the frequency in thevicinity of the sync signal tip portion of the luminance signal FM wavefor standard mode passes. On the other hand, since during the high bandmode no frequency component passes through the BPF 6, no signal wouldappear in the BPF output 7 (See FIGS. 3 and 4). In the event that a BPFoutput 7 is provided (during the standard mode), the wave detection iscarried out by the envelope detecting circuit 8 to obtain the wavedetected output 9. This signal is held in the hold circuit 10 for onehorizontal period whereby the hold circuit 10 provides the high banddiscriminating signal 11 as output. This high band discriminating signal11 is of a high level during the standard mode, and of a low levelduring the high band mode.

Accordingly, in such an embodiment, with the simple and inexpensiveapparatus such as the BPF and the wave detecting circuit, precise highband mode discrimination can be carried out, and by the utilization ofthe result of this discrimination, the mode changeover can beautomatically carried out.

It is to be noted that although the foregoing embodiment has beenconsidered wherein the discrimination is carried out in each horizontalsynchronizing signal portion, the discrimination may instead be doneonly during a period of a vertical synchronizing signal.

It is further noted that the present invention can be applicable notonly to VCR, but also to any magnetic recording and/or reproducingapparatus wherein the high band mode is automatically discriminated inreference to a level of the FM wave at a frequency in the vicinity of atip portion of the synchronizing signal.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

I claim:
 1. In a video signal magnetic recording/reproducing apparatus,a mode discriminating circuit which automatically discriminates theoriginal recording of a reproduced luminance signal FM wave in astandard mode or high band mode comprising:a bandpass filter, coupled tosaid reproduced luminance signal FM wave and of a selected bandpass,passing as a bandpass filter output frequencies in the vicinity of async signal tip portion of the reproduced luminance signal FM wave forsaid standard mode; an envelope wave detecting circuit, coupled to saidbandpass filter, providing a wave detected output in accordance withsaid bandpass filter output; and a hold circuit, coupled to saidenvelope wave detecting circuit, holding said wave detected output for apredetermined period of time to provide a discrimination signal of ahigh level indicative of said standard mode and of a low levelindicative of said high band mode.
 2. The mode discrimination circuit ofthe video signal magnetic recording/reproducing apparatus of claim 1wherein discrimination is carried out in each of a horizontalsynchronizing signal portion.
 3. The mode discrimination circuit of thevideo signal magnetic recording/reproducing apparatus of claim 1 whereindiscrimination is carried out in each of a vertical synchronizing signalportion.
 4. In a video signal magnetic recording/reproducing apparatus,a mode discriminating circuit which automatically discriminates theoriginal recording of a reproduced luminance signal FM wave in astandard mode or high band mode comprising:a bandpass filter, coupled tosaid reproduced luminance signal FM wave and of a selected bandpass,passing as a bandpass filter output frequencies in the vicinity of async signal tip portion of the reproduced luminance signal FM wave ofone of said modes; an envelope wave detecting circuit, coupled to saidbandpass filter, providing a wave detected output in accordance withsaid bandpass filter output; and a hold circuit, coupled to saidenvelope wave detecting circuit, holding said wave detected output for apredetermined period of time to provide a discrimination signal of ahigh level indicative of said one of said modes and of a low levelindicative of the other of said modes.
 5. A method of discriminating anoriginal recording of a reproduced luminance signal FM wave in astandard mode or a high band mode in a magnetic recording/reproducingapparatus comprising:passing, as a bandpass filter output, frequenciesof said reproduced luminance signal FM wave in the vicinity of the syncsignal tip portion of said standard mode; envelope wave detecting saidbandpass filter output to provide an envelope detected output; andholding said envelope detected output for a predetermined period of timein order to generate a discrimination signal of high level indicative ofsaid standard mode and of a low level indicative of said high band mode.6. The method of discriminating of claim 5 wherein discrimination iscarried out in each of a horizontal synchronizing signal portion.
 7. Themethod of discriminating of claim 5 wherein discrimination is carriedout in each of a vertical synchronizing signal portion.
 8. A method ofdiscriminating an original recording of a reproduced luminance signal FMwave in a standard mode or a high band mode in a magneticrecording/reproducing apparatus comprising:passing, as a bandpass filteroutput, frequencies of said reproduced luminance signal FM wave in thevicinity of the sync signal tip portion of one of said modes; envelopewave detecting said bandpass filter output to provide a envelopedetected output; and holding said envelope detected output for apredetermined period of time in order to generate a discriminationsignal of high level indicative of said one of said modes and of a lowlevel indicative of the other of said modes.